Tank comprising a reinforcement member and method for manufacturing such a reinforcement member

ABSTRACT

A tank manufactured from a plastic material. The tank includes a reinforcement member. The reinforcement member includes a first portion made of a first material weldable to the plastic material of the tank and a second portion made of a second material having a tensile stress at break which is three to nine times larger than the tensile stress at yield of the first material. The second portion includes at least one through-hole, and the first material extends in the at least one through-hole and at opposite sides of the second portion adjacent the at least one through-hole.

FIELD OF THE INVENTION

The invention relates to a tank comprising a reinforcement member, inparticular a fuel or an additive tank for a vehicle, and to a method formanufacturing such a reinforcement member. The invention also relates toa reinforcement member for use in a tank, and to a method for assemblinga tank.

BACKGROUND

Fuel tanks assembled from two plastic shells are known, and may comprisea stabilizing column or wall in the internal volume of the tank in orderto limit deformations of the tank. Traditionally fuel systems inpassenger vehicles are designed to hold a specific amount of liquid fuelat a pressure essentially the same as the ambient pressure. With theintroduction of Hybrid vehicles and more specifically Plug in Hybrids,which are designed such that they could potentially go several monthswithout using fuel, it is in the interest of the system designers tohold pressure inside the fuel tank to limit the emissions that couldpotentially bleed through the activated carbon canister due to diurnalcycles. In addition, holding pressure ensures that the composition ofthe fuel stays the same during storage. However, the tanks must be maderesistant to this internal pressure. Therefore tank reinforcement can berealized by linking two opposite tank surfaces with each other using aninternal connecting member.

It is known to form a stabilizing connecting member in the form of apillar or wall using a first pillar or wall part.

The pillar may be made of two materials, comprising e.g. a first portionmade of a first material compatible with HDPE and a second portion of asecond material having a limited deformation and/or creep.

SUMMARY

The object of embodiments of the invention is to provide a tank with areinforcement member having an improved design in terms of volume and/ormaterial usage and/or long-term stress resistance. A further object isto provide an improved method for manufacturing such a reinforcementmember for use in a tank.

According to a first aspect of the invention there is provided a tankmanufactured from a plastic material. The tank comprises a reinforcementmember. The reinforcement member comprises a first portion made of afirst material weldable to the plastic material of the tank; and asecond portion made of a second material having a tensile stress atbreak which is three to nine times larger than the tensile stress atyield of the first material. The second portion comprises at least onethrough-hole, and the first material extends in said at least onethrough-hole and at opposite sides of said second portion adjacent saidat least one through-hole.

Such an embodiment will result in a sufficiently strong reinforcementmember capable of resisting permanent stresses that may occur in thetank, e.g. in a fuel tank of a sealed fuel system. Due to the presenceof at least one through-hole, a good interlocking between the first andthe second material is obtained, so that the reinforcement member may berelatively light and the weight of the tank may be reduced. Byintroducing a second material having a higher tensile stress, theelongation/shrinking of the reinforcement member may be reduced, even ifthe reinforcement member is exposed to a permanent stress generated forexample by a permanent internal tank pressure. By using a secondmaterial having a tensile stress at break which is three to nine timeshigher than the tensile stress at yield of the first material, there isprovided a good compromise between this good resistance to a permanentinternal tank pressure and a good impact resistance of the fuel tank,taking into account that in impact tests the objective is to break thereinforcement member in order to prevent any leakage of fuel after suchan impact. Such an improved impact resistance of the tank improves theoverall crash resistance of the car.

Preferably, the second material has a tensile stress at break which isfour to eight times larger than the tensile stress at yield of the firstmaterial. Surprisingly the inventors have discovered that such a ratiobetween the tensile stress of the first and second material providesoptimal results with regard to impact resistance and durability of thetank.

In a preferred embodiment, the first material is overmoulded on thesecond portion, and the second portion is interlocked with the firstportion through the at least one through-hole. In other words thethrough-hole(s) ensure an interlocking of the first part and the secondpart in an interlocking zone comprising the through-holes. Preferably,the reinforcement member is connected to an inner surface of the tankalong a connecting plane, and the at least one through-hole has an axiswhich is arranged substantially parallel to the connecting plane orunder a sharp angle with respect to the connecting plane. Preferably,the distance between the connecting plane and the at least onethrough-hole is less than 30 mm, more preferably less than 20 mm.

Preferably, the first material has a tensile stress at yield between 15and 30 MPa at 23° C., preferably between 20 and 25 MPa at 23° C., andthe second material has a tensile stress at break between 45 and 270 MPaat 23° C., preferably between 80 and 200 MPa at 23° C. The firstmaterial may comprise e.g. a polyethylene material or a polyamidematerial. The second material may comprise any one or more of thefollowing materials: polyoxymethylene (POM), preferably a fiberreinforced POM, such as a glass fiber and/or aramid carbon reinforcedPOM, Polyphenylene sulfide (PPS), Polyphthalamide (PPA), preferably afiber reinforced PPA, Polyether ether ketone (PEEK), Polyamide-imide(PAI), Polyaryletherketone (PAEK), metal.

Preferably, the second portion is a wall part with a plurality ofthrough-holes, and the first portion extends around said wall part andin said through-holes. In an exemplary embodiment, the second portion isa tube-like part having an outer surface and an inner surface and the atleast one through-hole between said outer surface and said innersurface, and the first material covers said inner and outer surface.

In a possible embodiment, the first portion and the second portion areshaped and dimensioned such that, seen in a section parallel to aconnecting plane between the reinforcement member and an inner surfaceof the tank or under a sharp angle with respect to the connecting plane,a surface area occupied by the first material is between 65 and 90% ofthe total surface area of said section, preferably between 75 and 85% ofthe total surface area; and a surface area occupied by the secondmaterial is between 10 and 35% of said total surface area of saidsection, preferably between 15 and 25% of the total surface area. Inother possible embodiments, there may be provided a plurality ofthrough-holes extending in different layers of the reinforcement member,said layers extending parallel to a connecting plane between thereinforcement member and the tank, wherein for each layer there may bedefined a central section passing through the centre of thethrough-holes in that layer. In such an embodiment, the first portionand the second portion may be shaped and dimensioned such that, seen inan overlay of said central sections through said plurality of layers, asurface area occupied by the first material is between 65 and 90% of thetotal surface area of said overlay, preferably between 75 and 85% of thetotal surface area; and a surface area occupied by the second materialis between 10 and 35% of said total surface area of said overlay,preferably between 15 and 25% of the total surface area. In other words,in such embodiments there is made an overlay of the different centralsections, and the percentages are calculated for the summed surfaceareas of second material in the overlay section, see also the embodimentof FIGS. 5A-E. Preferably the distance between the connecting plane andeach central section is less than 30 mm, more preferably less than 20mm.

According to a second aspect of the invention, there is provided a tankmanufactured from a plastic material, said tank comprising areinforcement member. The reinforcement member comprises a first portionmade of a first material weldable to the plastic material of the tank,and at least one second portion made of at least one second materialhaving a higher modulus of Young than the first material and/or atensile stress at break which is higher than the tensile stress at yieldof the first material. The first and second portion are shaped anddimensioned such that, seen in a section of the reinforcement member, asurface area occupied by the first material is between 65 and 90% of thetotal surface area of said section; and a surface area occupied by theat least one second material is between 10 and 35% of said total surfacearea.

Such an embodiment will result in a sufficiently strong reinforcementmember capable of resisting permanent stresses that may occur in thetank, e.g. in a fuel tank of a sealed fuel system. Due to the relativelow percentage of second stronger material, e.g. POM, the reinforcementmember will be relatively light so that the weight of the tank, andhence the emissions of a vehicle containing such a tank may be reduced.Also, by introducing a low percentage of second stronger material theelongation/shrinking of the reinforcement member may be reduced, even ifthe reinforcement member is exposed to a permanent stress generated forexample by a permanent internal tank pressure. The tensile stress atbreak, also called tensile strength or ultimate strength is the stressthat a material can withstand while being stretched or pulled beforefailing or breaking. The tensile stress at break is usually found byperforming a tensile test and recording the stress versus strain curve.The tensile stress at break, the yield stress and the E-modulus may beboth obtained from stress versus strain curves. In a preferredembodiment the first material has an E modulus between 200 and 1600 MPaat 23° C. and a tensile stress at break between 15 and 30 MPa at 23° C.,and the second material has an E modulus between 2000 and 3500 MPa at23° C. and a tensile stress at break between 45 and 270 MPa at 23° C. Inan exemplary embodiment, the first material is HDPE having e.g. an Emodulus of 900 MPa and a tensile stress at break between 15 and 30 MPaat 23° C., and the second material is a reinforced POM material havinge.g. a tensile stress at break between 100 and 200 MPa at 23° C.

Preferably, the at least one second portion is interlocked with thefirst portion in an interlocking zone; and the section is a sectionthrough a plane in said interlocking zone. In the context of theinvention the term interlocking refers to the fact that the shape of thefirst and the second portion is such that the shape resists the pullingapart of the first and the second portion. In case of deformation of thefirst/second material, the deformation will be reduced due to theinterlocking. Further, taking into account the ratio between the amountof first material and second material, a sufficient strength is obtainedwhilst limiting the stresses introduced in the reinforcement member dueto the presence of two materials.

In a possible embodiment, the at least one second portion comprises awall part with a plurality of through-holes, and the first portionextends around the wall part and in the through-holes. In other words,the through-holes ensure an interlocking of the first part and thesecond part in an interlocking zone comprising the through-holes. In apossible embodiment, the at least one second portion comprises atube-like part having an outer surface and an inner surface and aplurality of through-holes extending from said outer surface to saidinner surface, and the first portion extends around the inner and outersurface and in the through-holes. Also in such an embodiment, thethrough-holes ensure an interlocking of the first part and the secondpart in an interlocking zone comprising the through-holes. Preferably,the section having the above given ratio of first/second material is asection through at least a number of through-holes of the plurality ofthrough-holes.

Preferably, the reinforcement member is connected to an inner surface ofthe tank along a connecting plane, and the section extends in a planesubstantially parallel to the connecting plane. Preferably, the distancebetween the connecting plane and the section is less than 30 mm, morepreferably less than 20 mm. Preferably, the reinforcement member extendsover a certain length inside the tank, wherein along at least a part ofsaid length, seen in a cross section of the reinforcement member, asurface area occupied by the first material is between 65 and 90% of thetotal surface area of said section; and a surface area occupied by theat least one second material is between 10 and 35% of said total surfacearea. In other words, it is advantageous if the above mentioned ratiobetween the first and the second material applies for a slice of thereinforcement member having a minimum height. This minimum height ispreferably larger than 1 mm.

Preferably, the reinforcement member has a total height, and the atleast one second portion extends over at least 80% of the total height.The above mentioned ratio may be valid for the full height of the atleast one second portion, but may also be valid for only a slice of thesecond portion, depending on the desired properties of the reinforcementmember.

In a preferred embodiment, the first portion and at least one secondportion are shaped and dimensioned such that, seen in the section of thereinforcement member, a surface area occupied by the first material isbetween 75 and 85% of the total surface area, more preferably between 78and 84% of the total surface area; and a surface area occupied by the atleast one second material is between 15 and 25% of the total surfacearea, more preferably between 16 and 22% of the total surface area.

In a preferred embodiment, the tank, in particular a fuel tank or anadditive tank for a vehicle, comprises a first shell and a second shell;wherein edges of said first and second shell are mutually connected suchthat said first and second shell together form a container delimiting aninternal volume. A connecting member is provided inside the tank andextends between the first shell and said second shell. The connectingmember comprises the reinforcement member. The reinforcement member maybe welded to the first shell and/or to the second shell.

In a preferred embodiment, the first shell is a top shell of the tankand the second shell is a bottom shell of the tank.

Embodiments of the invention are particularly useful for gasoline fueltanks because of the high pressure that may reign in such tanks.However, embodiments of the invention may also be used in other fueltanks, in additive tanks, in particular tanks for diesel additives, suchas urea tanks, etc. Also in applications where depressurization mayoccur, tanks according to embodiments of the invention will be useful.

The term “fuel tank” is understood to mean a substantially impermeabletank that can store fuel under diverse and varied environmental andusage conditions. The fuel tank according to the invention is preferablymade of plastic, that is to say made of a material comprising at leastone synthetic resin polymer. Particularly suitable are plastics thatbelong to the category of thermoplastics. The term “thermoplastic” isunderstood to mean any thermoplastic polymer, including thermoplasticelastomers, and blends thereof. The term “polymer” is understood to meanboth homopolymers and copolymers (especially binary or ternarycopolymers). Examples of such copolymers are: random copolymers, linearblock copolymers, other block copolymers and graft copolymers. Onepolymer often employed is high-density polyethylene (HDPE). However,excellent results may also be obtained with polyamide. Preferably, thetank also comprises a layer of a fuel-impermeable resin such as, forexample, EVOH (a partially hydrolysed ethylene/vinyl acetate copolymer).Alternatively, the tank may be subjected to a surface treatment(fluorination or sulphonation) for the purpose of making it impermeableto fuel. A multilayer fuel tank comprising an EVOH layer between twoHDPE layers is successfully used in the frame of the invention.

In preferred embodiments, the connecting member connects two oppositewall portions of the tank, i.e. wall portions facing each other, namelya first wall portion being part of the first shell and a second wallportion being part of the second shell. Preferably, these are a lowerwall portion (the one mounted facing downwards in the vehicle and whichis likely to creep under the weight of the fuel) and an upper wallportion (the one mounted facing upwards and subject to little or nocreep during use).

The connecting member (comprising one or more reinforcement members, orconsisting of the reinforcement member) is by definition rigid, i.e.over the life of the tank, it does not deform by more than a few mm,ideally by less than 1 mm. By “deformation” in meant in fact, a changeof the length thereof in the sense that it would space away or approachthe two tank shells.

According to another aspect of the invention, there is provided a methodfor manufacturing a reinforcement member for a tank manufactured from aplastic material. The method comprises providing a second portion of asecond material comprising at least one through-hole; and overmouldingsaid second portion with a first material such that said first materialextends in said at least one through-hole and at opposite side of saidsecond portion adjacent said at least one through-hole. The firstmaterial and the second material are chosen such that said secondmaterial has a tensile stress at break which is three to nine timeslarger than the tensile stress at yield of the first material, and suchthat the first material is weldable to said plastic material of thetank.

Preferably, the reinforcement member is connected to an inner surface ofthe tank along a connecting plane, wherein the distance between theconnecting plane and the at least one through-hole is less than 30 mm,preferably less than 20 mm. In an advantageous embodiment, thereinforcement member is connected to an inner surface of the tank alonga connecting plane, and the at least one through-hole is arrangedsubstantially parallel to the connecting plane or under a sharp anglewith respect to the connecting plane.

In a typical embodiment, the at least one second material is provided inthe form of a wall part with a plurality of through-holes spreadregularly over a one or more sections of the wall part, and the firstmaterial is overmoulded around the wall part and in the plurality ofthrough-holes.

In a preferred embodiment, the second portion is overmoulded with firstmaterial such that, seen in a section parallel to a connecting planebetween the reinforcement member and an inner surface of the tank orunder a sharp angle with respect to the connecting plane, a surface areaoccupied by the first material is between 65 and 90% of the totalsurface area of said section, preferably between 75 and 85% of the totalsurface area; and a surface area occupied by the second material isbetween 10 and 35% of said total surface area of said section,preferably between 15 and 25% of the total surface area. In otherpossible embodiments, there may be provided a plurality of through-holesextending in different layers of the reinforcement member, said layersextending parallel to a connecting plane between the reinforcementmember and the tank, wherein for each layer there may be defined acentral section passing through the centre of the through-holes in thatlayer. In such an embodiment, the first portion and the second portionmay be shaped and dimensioned such that, seen in an overlay of saidcentral sections through said plurality of layers, a surface areaoccupied by the first material is between 65 and 90% of the totalsurface area of said overlay, preferably between 75 and 85% of the totalsurface area; and a surface area occupied by the second material isbetween 10 and 35% of said total surface area of said overlay,preferably between 15 and 25% of the total surface area.

The first and second material may have the properties disclosed above inconnection with embodiments of the tank.

According to another aspect of the invention, there is provided a methodfor manufacturing a reinforcement member for a tank manufactured from aplastic material. The method comprises providing a first material and atleast one second material; each second material having a tensile stressat break which is higher than the stress at yield of the first materialand/or having a higher modulus of Young than the first second material,and said first material being weldable to said plastic material of thetank. The at least one second material is connected to the firstmaterial by overmoulding, in order to obtain the reinforcement member,wherein the overmoulding is performed such that, seen in a section ofthe obtained reinforcement member, a surface area occupied by the firstmaterial is between 65 and 90% of the total surface area of saidsection; and a surface area occupied by the at least one second materialis between 10 and 35% of the total surface area.

In a preferred embodiment, the first material and the at least onesecond material are overmoulded in such a way that an interlockingbetween said first material and said at least one second material isobtained in an interlocking zone; wherein the section is a sectionthrough a plane of the interlocking zone.

In a possible embodiment, the at least one second material may beprovided in the form of a wall part with a plurality of through-holes,and the first material is overmoulded around the wall part and in theplurality of through-holes. In a possible embodiment, the at least onesecond material is provided in the form of a tube-like part having anouter surface and an inner surface and a plurality of through-holesextending from said outer surface to said inner surface, and the firstmaterial is overmoulded on the inner and outer surface and in thethrough-holes. Preferably, the section is a section through at least anumber of through-holes of the plurality of through-holes.

In a preferred embodiment, the reinforcement member is connected, e.g.welded to an inner surface of the tank in a connecting plane, and thesection extends in a plane substantially parallel to the connectingplane, preferably at a distance smaller than 30 mm from the connectingplane. Preferably, the reinforcement member extends over a certainlength inside the tank, wherein along at least a part of said length,seen in a section of the reinforcement member parallel to the connectingplane, a surface area occupied by the first material is between 65 and90% of the total surface area; and a surface area occupied by the atleast one second material is between 10 and 35% of the total surfacearea.

In a preferred embodiment the overmoulding is performed such that, seenin a section of the reinforcement member, a surface area occupied by thefirst material is between 70 and 85% of the total surface area, morepreferably between 78 and 84% of the total surface area; and a surfacearea occupied by the at least one second material is between 15 and 30%of the total surface area, more preferably between 16 and 22% of thetotal surface area.

In a particular embodiment, the second portion made of a second materialhas a tensile stress at break which is three to nine times larger thanthe tensile stress at yield of the first material, and the first andsecond portion are shaped and dimensioned such that, seen in a sectionof the reinforcement member, a surface area occupied by the firstmaterial is between 65 and 90% of the total surface area of saidsection; and a surface area occupied by the at least one second materialis between 10 and 35% of said total surface area. The relationship givenabove can be expressed by a by-product which upper limit is given by theproduct between the maximum tensile stress at break of the secondmaterial and the maximum surface area occupied by the second material,and which lower limit is given by the product between the lower tensilestress at break of the second material and the lower surface areaoccupied by the second material. In this particular embodiment, theby-product is between 0.3 and 3.15.

Also the invention relates to a method for assembling a tank comprisingproviding a first shell and a second shell; putting edges of the firstand second shell into contact with each other and mutually connectingsaid edges such that the first and second shells together form acontainer delimiting an internal volume; providing the first shell witha connecting member extending inwardly from an inner surface of thefirst shell, said connecting member comprising a reinforcement memberthat is being manufactured according to any one of the above disclosedembodiments of the method; and connecting the connecting member to thesecond shell. The edges of the shells are preferably formed by flanges.Typically the shells are made of plastic, and typically the edges of theshells are welded to each other.

According to yet another aspect, the invention relates to a tankassembled according to any one of the above disclosed assembly methods.

Finally the invention relates to a reinforcement member for use in tankor for use in a method for manufacturing a tank, wherein thereinforcement member may be provided with any of the above disclosedfeatures.

Although certain features have been described only in connection withembodiments of the tank, the skilled person understands thatcorresponding features may be present in the method, and vice versa.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying drawings are used to illustrate presently preferrednon-limiting exemplary embodiments of devices of the present invention.The above and other advantages of the features and objects of theinvention will become more apparent and the invention will be betterunderstood from the following detailed description when read inconjunction with the accompanying drawings, in which:

FIG. 1A illustrates a side view of a second portion of a firstembodiment of a reinforcement member of the invention (beforeovermoulding), and FIG. 1B illustrates a cross section along BB of thereinforcement member including the first and the second portion (afterovermoulding);

FIG. 2A illustrates a side view of a second portion of a secondembodiment of a reinforcement member of the invention (beforeovermoulding), and FIGS. 2B and 2C illustrate a cross section along BBof the reinforcement member including the first and the second portion(after overmoulding) for two variants (with and without clips);

FIG. 3A illustrates a side view of a second portion of a thirdembodiment of a reinforcement member of the invention (beforeovermoulding), and FIG. 3B illustrates a cross section along BB of thereinforcement member including the first and the second portion (afterovermoulding);

FIG. 4A illustrates a schematic perspective view of a second portion ofa fourth embodiment of a reinforcement member of the invention (beforeovermoulding), FIG. 4B illustrates a cross section along BB of thereinforcement member including the first and the second portion (afterovermoulding), and FIG. 4C illustrates a schematic perspective view ofthe fourth embodiment;

FIG. 5A illustrates a perspective view of a reinforcement memberaccording to a fifth embodiment; FIGS. 5B-D illustrate a cross sectionsalong BB, CC, DD of the reinforcement member; and FIG. 5E represents anoverlay of the cross sections of FIGS. 5B-D.

FIG. 6 illustrates a cross section of a sixth embodiment of thereinforcement member; and

FIG. 7 illustrates an embodiment of a tank assembly including tworeinforcement members.

DESCRIPTION OF EMBODIMENTS

FIGS. 1A-1B illustrate schematically a first embodiment of areinforcement member 100 for a tank manufactured from a plasticmaterial, in particular a fuel tank or an additive tank, of theinvention. The reinforcement member 100 comprises a first portion 110made of a first material M1 that is weldable to the plastic material ofthe tank, and a second portion 120 made of a second material M2 having ahigher tensile stress at break and/or modulus of Young than the firstmaterial M1. FIG. 1A shows only the second portion 120 which is atube-like part in the form of a pillar. This pillar is overmoulded bythe first material M1 to form the reinforcement member 100. This isvisible in the cross section of FIG. 1B which shows that that firstmaterial M2 is overmoulded on the outer surface and inner surface of thesecond portion 120 and in through-holes 122 in the pillar. Asillustrated, the pillar may be provided with reinforcement ribs 121 toprovide additional strength.

The provision of through-holes 122 results in an interlocking functionbetween the first portion 110 and the second portion 120. Indeed, thanksto the through-holes 122, the second portion 120 is securely lockedbetween an outer and inner skirt 111, 112 of the first portion 110. Thedimensions of the first portion 110 and the second portion 120 arechosen such that, seen in a cross section at the level of theinterlocking, i.e. at the level of the plurality of through-holes 122, asurface area occupied by the first material M1 is between 65 and 90%,preferably between 75% and 85% (e.g. approximately 80%) of the totalsurface area of the section; and a surface area occupied by the secondmaterial M2 is between 10 and 35%, preferably between 15 and 25% (e.g.approximately 20%) of the total surface area. Surprisingly, theinventors have found that such a ratio provides a good strength whilstlimiting the stresses between the first portion and the second portion.

A first overmoulded end part 123 of the reinforcement member 100 isintended for being connected to an inner surface of the tank along aconnecting plane, and a second end part 124 is intended for beingconnected to an opposite inner surface of the tank. Preferably, thethrough-holes 122 extend substantially parallel to the connectingplanes.

FIGS. 2A-2C illustrate a second embodiment of a reinforcement member 200for a tank. The reinforcement member comprises a first portion 210 of afirst material M1 and a second portion 220 of a second material M2having a higher tensile stress at break and/or modulus of Young than thefirst material M1. In the second embodiment, the second portion 220takes the form of a wall part with a central recess. In an upper part224, as well as in a lower part 223 there is provided a plurality ofthrough-holes 222, spaced at regular intervals along the width of thewall part 220. Also the wall part 220 is provided with reinforcementribs 221, 225. This wall part 220 is overmoulded by the first materialM1 to form the reinforcement member 200. This is visible in the crosssection of FIGS. 2B and 2C which show that the first portion 210 extendsaround the wall part 220 and in the through-holes 222.

As in the first embodiment, the provision of through-holes 222 resultsin an interlocking function between the first portion 210 and the secondportion 220. Indeed, thanks to the through-holes 222, the second portion220 is securely locked between a first and second outer layer of thefirst portion 210. The dimensions of the first portion 210 and thesecond portion 220 are chosen such that, seen in a cross section at thelevel of the interlocking, i.e. at the level of the plurality ofthrough-holes 222 in the lower part 223 or in the upper part 224, asurface area occupied by the first material M1 is between 65 and 90%,preferably between 75% and 85% (e.g. between 81% and 84%) of the totalsurface area of the section, and a surface area occupied by the secondmaterial M2 is between 10 and 35%, preferably between 15 and 25% (e.g.approximately 16% and 19%) of the total surface area. This results in acompact reinforcement member having an excellent long term stressresistance.

In the second embodiment, the reinforcement member 200 is provided atits side with clips for mutually connecting adjacent reinforcementmembers 200. In that way there may be provided a number of mutuallyinterconnected reinforcement members 200 in the same tank.

The third embodiment, illustrated in the FIGS. 3A-3B, is similar to thesecond embodiment with this difference that no clips are provided. As inthe second embodiment, the reinforcement member 300 comprises a firstportion 310 formed as an overmoulded portion of a first material M1 overa second portion 320 of a second material M2, wherein the second portion320 is provided with through-holes 322 and reinforcement ribs 321.

FIGS. 4A-C illustrate a fourth embodiment of a reinforcement member 400for use inside a tank. The reinforcement member 400 comprises a secondportion 420 of a second material M2, and a first portion 410 of a lessstrong first material M1. The second portion 420 is shown in FIG. 4A andtakes the form of a tube like part with a rectangular cross section. Thetube-like part 420 is provided at an upper end with two rows ofthrough-holes 422, each row comprising a plurality of through-holes 422spread regularly along a circumferential zone of the tube-like part 420.The second portion 420 has a height h1. The overmoulded reinforcementmember 400 has a height h2, see FIG. 4C. Preferably, the height h1 is atleast 80% of the height h2. In the fourth embodiment only the upper partof the reinforcement member is provided with an interlocking zone as aconsequence of the through-holes 422. Such a reinforcement member 400may be useful in a tank where the connecting member is formed by anupper member connected to a lower member, see also FIG. 7, wherein afirst reinforcement member 400 may connected to an upper shell of thetank and a second reinforcement member 400 to a lower shell.

FIGS. 5A-E illustrate a fifth embodiment of a reinforcement member 500for use inside a tank. The reinforcement member 500 comprises a secondportion 520 (not visible in FIG. 5A) of a second material M2, and afirst portion 510 of a less strong first material M1. There are provideda plurality of through-holes (not shown) extending in different layersof the reinforcement member (layers B, C, and D), said layers extendingparallel to a connecting plane 530 for connecting the reinforcementmember to an inner wall of the tank. For each layer A, B, C there may bedefined a central section (shown in FIGS. 5B, 5C and 5D) passing throughthe centre of the through-holes 522A, 522B, 522C in that layer A, B, C,respectively. In such an embodiment, the first portion 510 and thesecond portion 520 may be shaped and dimensioned such that, seen in anoverlay (FIG. 5E) of said central sections, a surface area occupied bythe first material M1 is between 65 and 90% of the total surface area ofthe overlay, preferably between 75 and 85% of the total surface area;and a surface area occupied by the second material M2 is between 10 and35% of said total surface area of the overlay, preferably between 15 and25% of the total surface area, more preferably between 17% and 23%. Thesurface area of the second material takes into account all portions ofsecond material (the 7 squares in FIG. 5E) in all interlocking layers.Indeed, all those portions will influence the impact resistance anddurability, and the surface area of the second material is calculatedtaking into account the sum of all portions in the overlay.

In the fifth embodiment only the upper part of the reinforcement memberis provided with an interlocking zone with a plurality of interlockinglayers, but the skilled person understands that also the lower part maybe provided with an interlocking zone as in the first, second and thirdembodiment. Moreover, the interlocking zone in the upper part may be thesame as or different from the interlocking zone in the lower part.

FIG. 6 illustrates a sixth embodiment comprising a tube like secondportion of a second material M2 surrounded by a first portion of a firstmaterial M1. The interlocking is achieved through a dovetail connection.In the illustrated embodiment, the second portion is provided withdovetail ribs, but the skilled person understands that the secondportion could also be provided with dovetail grooves.

FIG. 7 illustrates schematically a tank assembly comprising a firstshell 701 and a second shell 702, wherein edges 703 of said first andsecond shell are mutually connected, typically welded, such that saidfirst and second shell together form a container delimiting an internalvolume. Inside the tank there is provided a connecting member 700 a, 700b extending between the first shell 701 and the second shell 702. In theillustrated embodiment, the connecting member comprises an upperreinforcement member 700 a with a second portion 720 a and a lowerreinforcement member 700 b with a second portion 720 b. The lowerreinforcement member 700 b has a lower end 723 b connected to an innersurface of the lower shell 702, and the upper reinforcement member 700 ahas an upper part 724 a connected to an inner surface of the upper shell701. In the assembled state the lower part 723 a of the upperreinforcement member 700 a is connected to the upper part 724 b of thelower reinforcement member 700 b. Alternatively the connecting membermay consist of one reinforcement member. The reinforcement member(s) maybe designed according to any of the above disclosed embodiments. Thefirst shell and/or the second shell of the tank may be moulded by anyone of the following techniques or by a combination of those techniques:injection moulding, compression moulding, injection-compressionmoulding, thermoforming, blow moulding, extrusion blow moulding,co-injection moulding.

In the above disclosed embodiments, the tank material may be e.g. apolyethylene material and the first material M1 may also be apolyethylene material. The second material M2 may be e.g. any one of thefollowing: POM, PPS, PPA, PEEK, PAI, PAEK, metal, wherein any of thosematerials may be optionally fiber reinforced.

Finally it is noted that embodiments of the invention may be combinedwith prior art techniques for arranging a connecting member in the tank.For example, there could be arranged a first reinforcement member in thetank in accordance with embodiments of the invention, and a secondreinforcement member integrally moulded with the first shell having anend part that is connected to the second shell.

Whilst the principles of the invention have been set out above inconnection with specific embodiments, it is to be understood that thisdescription is merely made by way of example and not as a limitation ofthe scope of protection which is determined by the appended claims.

The invention claimed is:
 1. A tank manufactured from a plasticmaterial, the tank comprising: a reinforcement member, the reinforcementmember comprising: a first portion made of a first material weldable tothe plastic material of the tank; a second portion made of a secondmaterial having a tensile stress at break which is three to nine timeslarger than the tensile stress at yield of the first material; whereinthe second portion comprises at least one through-hole, and the firstmaterial extends in the at least one through-hole and at opposite sidesof the second portion adjacent the at least one through-hole; whereinthe first portion and the second portion are shaped and dimensioned suchthat, seen in a section parallel to a connecting plane between thereinforcement member and an inner surface of the tank, a surface areaoccupied by the first material is between 65 and 90% of the totalsurface area of said section; and a surface area occupied by the secondmaterial is between 10% and 35% of said total surface area of saidsection.
 2. The tank of claim 1, wherein the second material has atensile stress at break which is four to eight times larger than thetensile stress at yield of the first material.
 3. The tank of claim 1,wherein the first material is overmolded on the second portion, and thesecond portion is interlocked with the first portion through the atleast one through-hole.
 4. The tank of claim 1, wherein distance betweenthe connecting plane and the at least one through-hole is less than 30mm.
 5. The tank of claim 1, wherein the first material has a tensilestress at yield between 15 and 30 MPa at 23° C., and the second materialhas a tensile stress at break between 45 and 270 MPa at 23° C.
 6. Thetank of claim 1, wherein the first material is a polyethylene materialor a polyamide material.
 7. The tank of claim 1, wherein the secondmaterial comprises at least one or more of the following materials:polyoxymethylene (POM), a fiber reinforced POM, Polyphenylene sulfide(PPS), Polyphthalamide (PPA), a fiber reinforced PPA, Polyether etherketone (PEEK), Polyamide-imide (PAI), Polyaryletherketone (PAEK), metal.8. The tank of claim 1, wherein a plurality of through-holes extend indifferent layers of the reinforcement member, the layers extendingparallel to a connecting plane between the reinforcement member and thetank, wherein each layer has a central section passing through thecenter of the through-holes in that layer, wherein the first portion andthe second portion are shaped and dimensioned such that, seen in anoverlay of the central sections through the plurality of layers, asurface area occupied by the first material is between 65 and 90% of thetotal surface area of the overlay; and a surface area occupied by thesecond material is between 10 and 35% of the total surface area of theoverlay.
 9. The tank of claim 1, further comprising: a first shell and asecond shell; wherein edges of the first shell and the second shell aremutually connected such that the first shell and the second shelltogether form a container delimiting an internal volume; a connectingmember provided inside the tank, the connecting member extending betweenthe first shell and the second shell; and the connecting membercomprising the reinforcement member.
 10. The tank of claim 9, whereinthe reinforcement member is welded to the first shell, or to the secondshell, or to the first shell and the second shell.
 11. The tank of claim1, wherein the reinforcement member is connected to an inner surface ofthe tank along a connecting plane, and wherein the at least onethrough-hole has an axis which is arranged parallel to said connectingplane.
 12. A method for manufacturing a reinforcement member for a tankmanufactured from a plastic material, the method comprising: providing asecond portion of a second material including at least one through-hole;overmolding the second portion with a first material such that the firstmaterial extends in the at least one through-hole and at opposite sidesof the second portion adjacent the at least one through-hole; whereinthe first portion and the second portion are shaped and dimensioned suchthat, seen in a section parallel to a connecting plane between thereinforcement member and an inner surface of the tank, a surface areaoccupied by the first material is between 65 and 90% of the totalsurface area of said section; and a surface area occupied by the secondmaterial is between 10% and 35% of said total surface area of saidsection; and wherein for the first material and the second material, thesecond material has a tensile stress at break which is three to ninetimes larger than the tensile stress at yield of the first material, andsuch that the first material is weldable to the plastic material of thetank.
 13. The method of claim 12, wherein the distance between theconnecting plane and the at least one through-hole is less than 30 mm.14. A method for assembling a tank comprising: providing a first shelland a second shell; putting edges of the first shell and the secondshell into contact with each other and mutually connecting the edgessuch that the first shell and the second shell together form a containerdelimiting an internal volume; providing the first shell with aconnecting member extending inwardly from an inner surface of the firstshell, the connecting member comprising a reinforcement member that isbeing manufactured according to the method of claim 12; and connectingthe connecting member to the second shell.
 15. The method of claim 12,wherein the reinforcement member is connected to an inner surface of thetank along a connecting plane, and wherein the at least one through-holehas an axis which is arranged parallel to said connecting plane.
 16. Atank manufactured from a plastic material, the tank comprising: areinforcement member, the reinforcement member comprising: a firstportion made of a first material weldable to the plastic material of thetank; a second portion made of a second material; wherein the secondportion comprises at least one through-hole, and the first materialextends in the at least one through-hole and at opposite sides of thesecond portion adjacent the at least one through-hole; wherein the firstportion and the second portion are shaped and dimensioned such that,seen in a section parallel to a connecting plane between thereinforcement member and an inner surface of the tank, a surface areaoccupied by the first material is between 65 and 90% of the totalsurface area of said section; and a surface area occupied by the secondmaterial is between 10% and 35% of said total surface area of saidsection; and wherein a by-product between the tensile stress at break ofthe second material and the surface area occupied by the second materialover the total surface area of a section parallel to a connecting planebetween the reinforcement member and an inner surface of the tank isbetween 0.3 and 3.15.
 17. The tank of claim 16, wherein thereinforcement member is connected to an inner surface of the tank alonga connecting plane, and wherein the at least one through-hole has anaxis which is arranged parallel to said connecting plane.